The energy of electrons in solids has discontinuous values, and electrons are distributed on some discontinuous energy bands.The gap between the energy band of the valence electron and the energy band of the free electron is called the band gap or band gap.Therefore, the width of the band gap actually reflects the additional energy that the bound valence electrons must obtain to become free electrons.Silicon has a band gap width of 1.12 eV, while wide band gap semiconductor materials refer to those with a band gap width of 2.3 eV or moresemiconductor material , typicallysilicon carbide(SiC), gallium nitride (GaN), diamond and other materials.Wide band gap semiconductor materials are called the third generation semiconductor materials.
With the development of microwave devices and optoelectronic devices, the Ⅲ - Ⅴ family is expanding, but the development of electronics has put forward higher and higher requirements for devices, especially those requiring high power, high frequency, high speed, high temperature and working in harsh environments.For example, the monitoring system of high-performance military aircraft and supersonic PAG engine requires long-term operation at 300 ℃, while ordinary devices can only operate normally at 100 ℃: in interstellar navigation, the surface temperature of Mercury is 370 ℃ when it is close to the sun, while the surface temperature of Venus is higher, up to 450 ℃, and the pressure is 10sevenPa, however, the maximum operating temperature of the silicon battery is only 200 ℃. Although the GaAs battery can operate above 200 ℃, its efficiency is greatly reduced;The communication field also requires higher frequency and higher power, all of which cannot be met by existing Si devices or GaAs devices.In the spaceship, in order to reduce the temperature of the device to 125 ℃ that the Si device can tolerate, a cooling system must be equipped. If the device can work at 325 ℃, removing this cooling system can reduce the volume of the unmanned spacecraft by 60%.The demand of the times calls for the emergence of high temperature semiconductor materials.For those who study semiconductor materials, they are facing an exciting era, because the research on high-temperature semiconductors has made rapid progress in recent years.[1]
Limitations of silicon materials
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Silicon materials have always beenPower electronic devicesMain semiconductor materials used.The main reason is that people have already mastered the technology of low-cost, mass manufacturing, large size, low defect, high purity monocrystalline silicon materials and various subsequent semiconductor processing technologies, and human continuous research and development investment in silicon devices is also huge.However, all aspects of the performance of silicon devices have approached the theoretical limit determined by material properties with the improvement of their structural design and manufacturing process (although this limit has been broken through again and again with the continuous innovation of device technology). Many people believe that silicon devices will continue to improve and improvePower electronic deviceAnd the potential of system performance has been very limited.Therefore, more and more attention is paid to power electronic devices based on wide band gap semiconductor materials.
Development of Wide Band Gap Semiconductor Materials
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Due to its much wider band gap than silicon, wide band gap semiconductor materials generally have much higher critical avalanche breakdown electric field strength, carrier saturation drift speed, higher thermal conductivity and similarCarrier mobilityTherefore, power electronic devices based on wide band gap semiconductor materials (such as silicon carbide) will have much higher ability to withstand high voltage and much lower on state than silicon devicesresistance, better thermal conductivity and stability, and stronger resistance to high temperature and radiation. Many aspects of performance are improved by orders of magnitude.However, the development of wide band gap semiconductor devices has been subject to the difficulties of material refining, manufacturing and subsequent semiconductor manufacturing processes.
It was not until the 1990s that a breakthrough was made in the refining and manufacturing technology of silicon carbide materials and the subsequent semiconductor manufacturing process. At the beginning of the 21st century, the Schottky diode based on silicon carbide was introduced, which is superior to the Schottky diode based on silicon in performance. Therefore, it was rapidly applied in relevant power electronics devices,Its overall benefits far exceed the cost increase caused by the price difference between these devices and silicon devices.Gallium nitrideSince the 1990s, the semiconductor manufacturing process has also made a breakthrough, so it has also been possible to manufacture corresponding devices on the basis of other materials.GaN devices have attracted more attention because of their better high-frequency characteristics than silicon carbide devices.Diamond has the best performance among these wide band gap semiconductor materials, and many people call it the most ideal or promising power semiconductor materials.But diamond material refining and manufacturing and subsequent semiconductor manufacturing process are also the most difficult, and there is no effective method.There is still a long way to go before the emergence of power electronic devices based on diamond materials.[1]
application
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The Ill nitride (also called GaN based) semiconductor, which is composed of indium nitride (InN), gallium nitride (GaN), aluminum nitride (AIN) and their alloys, is the most important type of wide band gap semiconductor.Its main application fields include:
(1) Lighting field: currently, semiconductor lighting, which is very attractive at home and abroad, is a new type of efficient, energy-saving and environmentally friendly light source. It will replace most of the traditional light sources used and is known as the revolution of lighting sources in the 21st centuryHigh brightness LEDThe development of LED is the core technology and foundation for realizing semiconductor lighting.
(2) Optical storage field: optical storage density of DVD and its application as read-write devicesemiconductor laser The square of the wavelength of GaAs is inversely proportional to the square of the wavelength of GaAs. The GaAs based short wavelength semiconductor laser can increase the DVD optical storage density of the GaAs based semiconductor laser currently used by 4-5 times. It will become the mainstream technology of new optical storage and processing.
(3) Electronic device field: High temperature, high frequency and high power microwave devices are urgently needed in wireless communication, national defense and other fields. If the output power density of microwave power tubes used is increased by an order of magnitude, and the operating temperature of microwave devices is increased to 300 ℃, a series of problems in aerospace electronic equipment and civil mobile communication systems will be solved.Silicon carbide is another representative of wide band gap semiconductor materials.The working temperature of silicon carbide can reach 600 ℃. Its excellent characteristics make it have broad application prospects in the development of high-temperature, high-frequency, high-power, radiation resistant devices, ultraviolet detectors, short wave light-emitting diodes and other aspects.[2]
